Abstract: "The heating of plane solid targets by the Vulcan petawatt laser at powers of 0.32-0.73 PW and intensities of up to 4x1020 W cm[?]2 has been diagnosed with a temporal resolution of 17 ps and a spatial resolution of 30 mm, by measuring optical emission from the opposite side of the target to the laser with a streak camera. Second harmonic emission was filtered out and the target viewed at an angle to eliminate optical transition radiation. Spatial resolution was obtained by imaging the emission onto a bundle of fibre optics, arranged into a one-dimensional array at the camera entrance. The results show that a region 160 mm in diameter can be heated to a temperature of [?]107 K (kT/e[?] keV) in solid targets from 10 to 20 mm thick and that this temperature is maintained for at least 20 ps, confirming the utility of PW lasers in the study of high energy density physics. Hybrid code modelling shows that magnetic field generation prevents increased target heating by electron refluxing above a certain target thickness and that the absorption of laser energy into electrons entering the solid target was between 15-30%, and tends to increase with laser energy."